Marvin Friedman

Assessment of right ventricular anatomy and function by quantitative radionuclide ventriculography

Determination of right ventricular ejection fraction and volumes from radionuclide studies is cumbersome and is subject to considerable methodologic error. Further, assessment of regional wall motion has only infrequently been approached in a systematic way. A system of right ventricular ejection fraction and volume measurements is described that utilizes the previously validated single plane geometric method applied to first pass radionuclide angiocardiograms. Five right ventricular chords were defined and used to assess regional wall motion; normal values were obtained from 14 patients who were without demonstrable cardiac disease. Among 23 patients with anterior myocardial infarction, the right ventricular ejection fraction was within 2 SD of normal in 16; however, 3 of these patients showed regional wall motion abnormalities in the right ventricle. Of 21 patients with inferior myocardial infarction, right ventricular ejection fraction was reduced in 15; of the 6 with normal values, 3 had regional wall motion abnormalities as demonstrated by the chord shortening method. Of 21 patients with dilated cardiomyopathy, right ventricular function was abnormal in 20; the presence of a wall motion abnormality in the conus segment separated these patients from patients with right ventricular dysfunction after recent myocardial infarction. Thus: 1) right ventricular ejection fraction, volumes and wall motion can be assessed by a simple, geometric technique; 2) analysis of chord shortening by this method provides information unavailable from global ejection fraction data alone; and 3) the clinical correlates of these data will require further investigation.

Radiocardiography in clinical cardiology

Quantitative radiocardiography provides a variety of noninvasive measurements of value in cardiology. A gamma camera and computer processing are required for most of these measurements. The advantages of ease, economy, and safety of these procedures are, in part, offset by the complexity of as yet unstandaridized methods and incomplete validation of results. The expansion of these techniques will inevitably be rapid. Their careful performance requires, for the moment, a major and perhaps dedicated effort by at least one member of the professional team, if the pitfalls that lead to unrecognized error are to be avoided. We may anticipate more automated and reliable results with increased experience and validation.

Do patient data ever exceed the partial volume limit in gated SPECT studies

BackgroundSome single photon emission computed tomography (SPECT) methods to detect percent myocardial wall thickening (%WT) assume a linear relationship to changes in maximum myocardial counts, predicated on myocardial walls never exceeding the SPECT camera’s partial volume limit. Recent studies have challenged such assumptions, reporting that systolic count changes underestimate wall thickening as measured by echocardiography and magnetic resonance imaging.Methods and ResultsTo test whether clinical data ever are observed to exceed the partial volume limit, we examined gated tomograms of 75 patients selected at random and of an additional 25 patients known to have hypertension with electrocardiographic evidence of left ventricular hypertrophy. Image transformations were performed such that for every cinematic frame, radial counts at every angle were automatically normalized to the same maximum count. If no patient’s myocardium ever exceeded the partial volume limit, thickness quantified from transformed images would always be the same throughout the cardiac cycle and would just correspond to the camera’s line spread function. Thickness was measured by Gaussian fitting of transformed myocardial counts in the epicardial direction only to exclude cavitary count contamination. %WT was computed from thickness differences from diastole to systole. %WT values were assessed from clinical data at lateral, inferior, septal, anterior, and apical territories. Resulting %WT distributions were tested against the null hypothesis of %WT=0 by the Z-test. Although some distributions were not actually Gaussian, the maximum mean %WT was only +3%±5% for the septal wall, in agreement with an observer’s impressions of no detectable wall thickening. Thus mean %WT values were trivial compared with expected physiologic normal values of 30% to 50%.ConclusionNo convincing evidence was found of thickness above the partial volume limit in this large sample of 75 normotensive and 25 hypertensive patients. Therefore it is likely that relations between myocardial count increases and wall thickening are similar throughout the cardiac cycle, even in patients with left ventricular hypertrophy.

Cardiovascular nuclear medicine: An overview

Some of the available cardiovascular nuclear medicine methods are incompletely validated, and others are incompletely developed. They are, however, of very great potential in diagnostic cardiology, and in patient management. A new era of clinical research and acute care monitoring has been opened by serial, noninvasive, hemodynamic measurements of right ventricular as well as left ventricular function. Stress testing has become more specific, and should, with future developments, become more specific, and should, with future developments, become more sensitive, using radionuclide procedures. Serious quality control and validation questions concerning thallium stress testing must be addressed. Intracoronary injection of radiogases has great potential, although minimal present application. Emission computerized tomography will be an important research tool. Compartmental analysis modeling of first pass tracer injections has much to offer, but is not yet validated. Present growth rate of these procedures is very rapid. Fully developed, cardiovascular nuclear medicine may become the largest component of clinical nuclear medicine practice.

Measurement of regional myocardial perfusion using collimated miniature radiation detectors and the method of 133-Xenon washout

A new approach to the measurement of local myocardial perfusion based on the application of highly-collimated miniature cadmium telluride radiation detectors to measure washout of 133-Xenon from well-defined tissue volumes is presented. Single-hole collimators with length/diameter ratios of 1 (L=4 mm, D=4 mm) and 4 (L=12 mm, D=3 mm) were employed as prototype designs. The probe field of view was characterized theoretically using a spherical model of the myocardium in conjunction with experimental point source response measurements for each collimator. Method evaluation using two medium resolution collimators (L/D=1) was effected by performing left main and circumflex coronary artery perfusion studies at controlled but variable flows in the dog heart. An excellent correlation (r>0.99) between actual and estimated perfusion determined from 65 washout curves over the flow range 0.38 to 3.18 ml/min/gm was demonstrated. The ability to resolve regional flow differences was verified by measuring tracer washout from circumflex and left anterior descending regions of the myocardium, using two high resolution collimators (L/D=4), in a preparation where the left main coronary artery was cannulated and a snare was placed around the circumflex coronary artery to selectively reduce flow to that region.

Intense moving intestinal activity as a source of artifact on myocardial perfusion SPECT study

A 72-year-old male with a past medical history of non-ischemic cardiomyopathy, atrial fibrillation, mechanical mitral valve replacement, and severe peripheral vascular disease with chronic osteomyelitis of the left foot was admitted for chronic heart failure exacerbation and left leg pain. The patient required a below-knee amputation for chronic osteomyelitis of the left leg. A pharmacologic stress myocardial perfusion scan was performed as part of preoperative risk assessment. The patient underwent a single-day rest/stress protocol with regadenoson and Tc-99m sestamibi. Following the intravenous administration of 7.5 mCi of Tc-99m sestamibi with the patient at rest, SPECT was performed. Subsequently following the intravenous infusion of 0.4 mg of regadenoson, the patient received an additional intravenous dose of 23.1 mCi of Technetium99m sestamibi, and additional tomographic images were performed after a 1 hour delay. The patient experienced no chest pain, and there were no ST segment changes during regadenoson administration. SPECT images were processed with Wide Beam Reconstruction (WBR) reduced count density software to accommodate the reduced tracer activity administered to the patient. Review of tomographic images and polar plots revealed a small, severe, fixed apical defect with akinesis and absent wall thickening. Also noted was a reversible localized perfusion defect in the inferolateral wall (Figure 1A, B). Careful review of the rotating planar images in endless-loop cinematic format showed intense moving small bowel activity to the left of the heart in the x-plane (Figure 2). Because of the potential of artifact from moving bowel activity, the post-stress SPECT acquisition was repeated 1 hour later after the patient ingested 16 oz. of water. No significant bowel activity was present in this location in the repeat rotating planar images. Similarly the localized stress perfusion defect in the inferolateral wall was no longer present on tomographic images and polar plots (Figures 3, 4). The small bowel activity had shifted more inferiorly and rightward, still slightly in the x-plane of the heart, creating a minimal artifact in the inferior myocardial wall.